Microstructural features and strength properties of weak pyroclastic rocks from Central Italy

Large areas of Central and Southern Italy, where many historic towns are sited, are covered by pyroclastic materials. Their mechanical behaviour, at the border between weak rocks and granular soils, poses various problems in geotechnical modelling. The paper focuses on the results of an experimental study of the microstructural features and mechanical properties of three pyroclastic deposits: a weak pyroclastic rock from the Colli Albani Volcanic Complex, forming large areas of the subsoil of the city of Rome; one pozzolana and one tuff from the Vulsini Volcanic Complex, forming the slab on which the historical town of Orvieto is founded. The microstructural features are described with the aid of optical and electron scanning microscopy. The mechanical behaviour is investigated by means of a wide range of conventional uniaxial and triaxial compression. The paper discusses the results of the experimental micro-structural and geotechnical investiga-tion in order to find out common features among materials having the same depositional process and possible relationships between their microstructural features and strength.